The Guns of the Ironclad “Riachuelo”

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Written by: David Minshall

The Hex Bore project has a good archive / library of Whitworth research material, but now and again something new surfaces. 

‘The Guns of the Ironclad “Riachuelo” and Their Alteration to the Armstrong System’ is a treatise by Duarte Huet Bacellar Pinto Guedes, First Lieutenant of the Brazilian Navy.


In 1881 the contract for building the Brazilian battleship had been awarded to the London firm of Messrs. Samuda Bros. The Riachuelo was to be equipped with four 20 ton 9-inch turret guns and six 70-pounders, of 5.5 inch bore.

Both Armstrong and Whitworth tendered for the 20 ton guns (See Table I). The Brazilian Government had previously invested in Whitworth guns for several of their ships, and an order was placed with Sir Joseph Whitworth and Co. Limited. One of these Whitworth guns was subjected to trial on the sands at Southport (NW England) in August 1883. Results included penetration of an 18 inch wrought iron plate.


The Whitworth exceeded the articles of the contract in terms of velocity, penetration and range. Prior to the trial however, in June 1883 the Brazilian Government had approved a project that the naval armament be “all of the new Armstrong model.” 

The firm of Sir W.G. Armstrong, Mitchell, and Co. were asked for a proposal for the alteration of the Whitworth guns of hexagonal bore into guns of cylindrical grooved bore on the Armstrong principle. 

It was agreed that one of the guns for the Riachuelo should be sent to be altered by Armstrong, Mitchell and Co. This altered gun was subject to trial at Southport in January 1884.

The whole was timely, enabling comparison of two systems of artillery in order to decide upon one of them. This at a time the Brazilian Government were endeavouring to discover the best kind of armament for be acquired for the marine.

Conclusion was that the altered system was superior, and the Brazilian Government sanctioned the alteration of the guns of the Riachuelo.

The author of the technical treatise is critical of the process and presents a comparison of the Whitworth and Armstrong systems. Also include in this single volume book of 1885 are a series of articles that were published in the “Diario Official” from 20 March to 9 May, 1885.  This include numerous official Brazilian correspondence relating to the armament of the Riachuelo, and arguments to refute the findings of Lieutenant Bacellar. Finally a third paper is included, which is a reply by Bacellar to the article in the “Diario Official.” The whole is highly technical in parts with much mathematical analysis of the trails results.